Countersink attachment for twist drills



June 4, 1957 C. E. WRIGHT COUNTER SINK ATTACHMENT FOR TWIST DRILLS Filed July 19, 1954 lNvilhlTOR, V cHmges e. wrqgm' sv v AT T0 w In ow.

United States Patent COUNTERSINK ATTACHMENT FOR TWIST DRILLS Charles E. Wright, Toronto, Ontario, Canada Application July 19, 1954, Serial No. 444,286

3 Claims. (Cl. 145-125) This invention relates to a countersink for twist drills or bits and in particular to a one piece countersink which is mounted on the drill and which can be used with a wide range of drill sizes for producing a countersunk hole having the correct proportions relative to the size of the drill on which it is mounted.

Heretofore countersinks have been provided for use in combination with bits or drills for producing a countersunk drill hole, but it has been necessary to provide a separate countersink for each size of drill. Countersinks designed for mounting on a range of drill sizes have a multiplicity of parts which must be adjusted for each specific drill size with which it is employed.

It is an object of the present invention to provide a countersink of substantially unitary construction which is adapted for use with a Wide range of drill sizes. A further object of the invention is to provide a countersink which will serve as a depth gauge to limit the depth of the drilled hole to that required.

A further object is to. provide, without additional parts or appendages, means to regulate the dimensions of the countersunk hole to that required for the specific size of screw or bolt for which the hole is drilled. The size of the countersunk hole is variable, being in direct relation to the size of the drill upon which the countersink is mounted. That is, due to its eccentric rotation, the countersink stops cutting, even though it is still being rotated, when the correct size of the countersunk hole is reached for the diameter of the drill on which the countersink is mounted.

These and other objects are accomplished by the novel features of construction which are described in the following description and illustrated in the accompanying drawings in which:

Figure 1 is a perspective view of the countersink mounted on a small diameter drill.

Figure 2 is a bottom plan View of Figure 1 looking upwardly towards the cutting edge of the countersink.

Figure 3 is a front elevation of the countersink mounted on a drill of larger diameter than that shown in Figure 1.

Figure 4 is a bottom plan view of Figure 3 looking upwardly to the countersink.

Figure 5 is a cross section on the line 55 of Figure 2.

Figure 6 is a view of the countersink showing how the bearing surface is obtained.

Figure 7 is a plan view of a piece of material in which a series of countersunk holes has been produced by a single countersink.

The countersink of the present invention comprises a cylindrical shaped body 10 having a generally conical shaped head 11, a passageway 12 extending longitudinally therethrough, said passageway being substantially circular in transverse cross section. The wall of the passageway 12 is designed to form a seat 13 which extends the full length of the passage. This seat assists in properly aligning the countersink on the drill. Set screws 14 are entered through the wall of the body 10 opposite the seat 13 so that the screws project into the passageway 12 towards the seat. The drill is urged against and held firmly in the seat 13 by the screws 14.

The cutting edge 16 is formed in the head 11 and ex tends from the seat 13 to the periphery of the base of the conical head. The cutting edge 16 preferably extends tangentially relative to the periphery of the passageway 12 from the point at which the seat and the periphery of the passageway meet to the periphery of the base of the conical head. A bearing surface having a substantial angle of positive clearance behind the cutting edge at the end of the cutting edge adjacent the passageway, said angle of clearance decreasing progressively to become a negative angle of clearance behind the cutting edge adjacent the other end of the cutting edge. As illustrated in Figure 6, the bearing surface can be formed by grinding the conical head as to decline or fall away from the cutting edge starting at the end nearest the passage 12 adjacent the seat 13 at a decreasing angle until at the outside end of the said cutting edge of the angle decreases to zero with relation to the horizontal plane, said decline continuing to a point diametrically opposite the seat 13. The conical head 11 in front of the cutting edge 16 is shaped to provide clearance for the material removed by the countersink. In operation, the bearing surface 17 bears on the wall of the countersunk hole in proportion to the degree of eccentricity in its rotation.

The seat 13 is of sufiicient depth so that drills of small diameter, for example A will seat therein to a greater extent than drills of larger diameter. The seat assists in the proper alignment of the countersink on the drill, particularly for the smaller diameter drills. Thus, when the countersink is mounted on a small drill it will have a greater eccentricity than when mounted on a drill of larger diameter. As the diameter of the drill approaches the capacity of the passage the eccentricity decreases. With a drill of the full capacity of the passageway, the drill and countersink will be substantially concentric.

The relationship between the bearing surface 17 and the eccentricity of the countersink is such that the bearing surface 17 comes into contact with the work progressively later as the size of the drill increases.

When the bearing surface of the countersink comes into contact with the work, it has the effect of lifting the cutting edge out of contact with the work and it will thus automatically stop cutting when a countersunk hole of the correct dimensions has been cut for the particular size drill on which it is mounted. Thus, when the countersink is at its greatest eccentricity relative to the drill, the effective area of the cutting edge is reduced by the bearing surface 17 coming into contact with the work at the earliest stage so that it will only make a small countersunk hole, the dimensions of which are inversely relative to the degree of eccentricity which, in turn is relative to the size of the drill. As the size of the drill increases, the amount of eccentricity decreases and the bearing surface 17 permits the countersink to penetrate further into the work and the size of the countersunk hole is increased accordingly.

The countersink which is shown in the drawings on an enlarged scale, has the passageway 12 of a size which will receive a drill but is shown in Figures 1, 2 and 5 as being mounted on a /8 drill to illustrate the eccentricity. Figures 1 and 2 show that the drill and countersink have drilled a countersunk hole into the piece of wood identified by the numeral 18.

The combined effect of the foregoing construction is that the same countersink can be used for all sizes of drills from the smallest size to the full capacity determined by the diameter of the passageway 12 and that the countersink will cease cutting when the hole has been properly countersunk relative to the size of the drill on which it is mounted. Furthermore, when the countersunk hole has been formed, it is not possible for the drill'to advance further into the material due to the action of the bearing surface 17. It is thus seen that the countersink 1' of the', present invention automatically makes a countersunk hole of desired dimensions forithe'drill on which it is mounted. Also, as thesurface 17 bears against the inside surface of 'the countersunk hole, the limiting efiect does not mar the exposed surface of the work.

The countersink also serves as a depth gauge. This is efiected by the vertical position of the countersink on the drill which provides that the depth of the drilled hole can be no greater than the distance from the countersink to the point of the drill plus the countersink.

i 'What I claim as new and desire to protect by Letters Patent of the United States is:

1. A countersink .for twist drills and the like which comprises a body having a generally conical shaped head, a passageway extending longitudinally through said body of a diameter sufiicient to accommodate a drill within a predetermined size range up to and including that size which fits concentrically within the passageway, means for firmly securing a drill in said passageway, a cutting edge formed in the generally conical head and extending generally tangentially from the periphery of said passageway to the periphery of the head, a bearing surface having a substantial angle of positive clearance behind the cutting edge at the end of the cutting edge adjacent the passageway, said angle of clearance decreasing progressively to become a negative angle of clearance behind the cutting edge adjacent the other end of the cutting edge.

' 2. A countersink for twist drills and the like which comprises a body having a generally conical shaped head, a passageway extending longitudinally through said body of a diameter sufiicient to accommodate a drill within a predetermined size range up to and including that size which fits concentrically within the passageway, a seat formed in said passageway and extending longitudinally therethrough, means substantially diametrically opposite to said seat for firmly securing a drill in said seat, a cutting edge formed in the generally conical head and extending generally tangentially from the periphery of said passageway at a point adjacent to said seat to the periphery of the head, and a bearing surface having a substantial angle of positive clearance behind the cutting edge at the end of the cutting edge adjacent the passageway, said angle of clearance decreasing progressively to become a negative angle of clearance behind the cutting edge adjacent the other end of the cutting edge.

3. A one piece countersink for twist drills and the like i which comprises a body having a generally conical shaped head, a passageway extending longitudinally through said body of a diameter sufficient to accommodate a drill within a predetermined size range up to and including that size which fits concentrically within the passageway and in which drills of less diameter than the largest drill within the said predetermined range are seated eccentrically, a seat formed in said passageway and extending longitudinally therethrough, means for firmly securing a drill in said passageway, a cutting edge formed in the generally conical head and extending generally tangentially from the periphery of said passageway at a point adjacent to said seat to the periphery of the head, and a bearing surface having a substantial angle of positive clearance behind the cutting edge at the end of the cutting edge adjacent the passageway, said angle of clearance decreasing progressively to become a negative angle of clearance behind the cutting edge adjacentthe other end of the cutting References Cited in the file of this patent UNITED STATES PATENTS 

